The present invention is directed to bicycles and, more particularly, to various features of an electrically operated bicycle derailleur.
Derailleur operated bicycle transmissions typically comprise a plurality of sprockets that rotate with another rotating member (e.g., the front crank and/or the rear wheel of the bicycle) and a derailleur that is used to shift a chain among the plurality of sprockets. Conventional derailleurs comprise a base member adapted to be mounted to the bicycle frame, a movable member supporting a chain guide, and a linkage mechanism coupled between the base member and the movable member so that the movable member can move laterally inwardly and outwardly relative to the base member. Such derailleurs are controlled manually by a hand operated actuator such as a lever or twist-grip attached to the bicycle handlebar, wherein the derailleur is connected to the actuator by a Bowden cable.
Recently, various electronic devices have been developed to control the movement of the derailleur. Such devices sometimes comprise a traveling condition detector for detecting a traveling condition of the bicycle, a motor for moving the derailleur laterally inwardly and outwardly relative to the plurality of sprockets, and a processor. The processor controls the motor in response to the detected traveling condition so that the derailleur is placed in the proper position to maintain the traveling condition within a desired range.
The motor typically moves the derailleur laterally inwardly and/or laterally outwardly by moving an actuating member such as an actuating arm or a pivot shaft attached to the linkage mechanism. Unfortunately, sometimes the movable member experiences significant resistance to lateral movement, especially when the plurality of sprockets are stationary, and this resistance is communicated to the actuating member. Since the motor may be unable to move the actuating member in such a situation, there is a risk of damage to the motor. Another problem is the potential application of undesirable external forces to the movable member. Such external forces may be communicated to the actuating member, thereby risking damage to the motor. For example, an undesirable force directed toward the wheel may be applied to the derailleur when the bicycle falls down, or an undesirable force directed away from the wheel may be applied to the derailleur if the derailleur catches an external object.
To avoid damage to the derailleur, a clutch may be disposed in a power transmission path between the actuating member and the chain guide. The clutch may comprise first and second elements that disengage when significant resistance exists within the power transmission path. In some cases it may be necessary for the user to manually reengage the first and second members.